1. Field of the Invention
The present invention is directed to a stand alone battery module of juxtaposed electrochemical cells. A plurality of modules are in turn assembled together to form a battery pack. Although the cells may be of any type, lithium-ion cells are particularly suitable when the module is used in a battery pack for an electric vehicle.
2. Related Art
U.S. Pat. No. 5,378,555 to Waters et al. discloses an electric vehicle battery pack wherein a plurality of batteries are set in a supporting tray, and are mechanically connected together by interlocking plugs. The interlocking plugs include passages for electric connection between the batteries by cables, as well as for cooling tubes, and for wiring systems for the pack""s electronic controllers. However, the battery pack disclosed in Waters includes the disadvantages of having a large volume and complex mechanical, electrical, as well as thermal connections, between the batteries in the battery pack.
An object of the present invention is to overcome the disadvantages of the prior art. Another object of the present invention is to provide a battery module for retaining a plurality of electrochemical cells for convenient use as a battery. Another object is to provide a battery module having component parts which are easy to manufacture. A further object is to provide a battery module which is easy to assemble. A further object of the present invention is to provide a simply designed battery module which can accommodate different sized cells while eliminating rattle, maintaining a proper thermal operating temperature, and simple electrical connections. A further object is to provide a battery module having decreased volume and weight.
The stand alone battery module of the present invention includes a configuration which reduces the overall volume of the module as well as facilitates the connection of a plurality of modules to form a battery pack. Further, the configuration of the module reduces the overall weight of the module, thereby increasing the power to weight and energy to weight ratios of the module as well as that of any battery pack in which it is included. Moreover, the parts which make up the module are designed to facilitate their manufacture, as well as facilitate assembly of the module.
The stand alone battery module of the present invention includes: (a) a mechanical configuration; (b) a thermal management configuration; (c) an electrical connection configuration; and (d) an electronics configuration. Such a module is fully interchangeable in a battery pack assembly, mechanically, from the thermal management point of view, and electrically. With the same hardware, the module can accommodate different cell sizes and, therefore, can easily have different capacities because Saft cells are designed with the same diameter but different lengths for different capacities. The module structure is designed to accommodate the electronics monitoring, protection, and printed wiring assembly boards (PWAs), as well as to allow airflow through the module. A plurality of modules easily may be connected together to form a battery pack. The battery pack is especially useful as a power source for an electric vehicle.
a) Mechanical Configuration
In the battery module of the present invention, a cell assembly is formed of a plurality of cells which are held between a pair of cell holding boards which in turn are connected by tie rods, for example. The cells are aligned so that their longitudinal axes are parallel with one another, and are perpendicular to the holding boards. The cell assembly is contained within a shell. An end cap is then attached to each holding board with a space between the end cap and holding board. Within each end cap there are two ports. On one side of the module, the ports in one end cap are for air intake, whereas the ports in the opposite end cap are for exhaust. On the intake side, the space between the end cap and the holding board is an air manifold. Because the ports in the end caps are similar, either end cap may be the inlet or exhaust side of the module.
Each holding board includes a first side, a second side, and a thickness therebetween. On the first side are a plurality of cavities which extend into the holding board, but to an extent less than the thickness of the holding board, so as to form a cavity bottom. The peripheral shape of each cavity matches the peripheral shape of the cell to be held therein. Preferably the cells and cavities have a circular peripheral shape as such provides good reduction in volume of the module due to the ease in nesting of the cells with one another. A plurality of cavities are aligned along the length of the holding board to form a first line. A second line includes a plurality of cavities which are staggered with respect to the cavities of the first line. A third line includes a plurality of cavities which are staggered with respect to the cavities of the second line, but are aligned with respect to the cavities of the first line. The foregoing arrangement of circular cavities allows the cells to easily nest with one another thereby reducing the overall volume of the module. Because the second line is offset from both the first and third line, it forms in the module a protrusion on one side and a recess on the other side. The protrusion and recess assist in locking modules together to form a battery pack having an overall reduced volume, as well as increased stability. That is, when the protrusion on one module is aligned with the recess on an adjacent module, the modules nest together, and are stably held with respect to one another while producing an overall minimum volume for the battery pack.
Within the periphery of each cavity there is a first through hole which accommodates a terminal of the cell held by the cavity. Some of the cavities also include a second through hole which accommodates a fill tube of the cell. The second through hole is in the cavities which hold the negative end of the cell because that end of the cell includes the fill tube. The cavity bottom may include a recessed portion to accommodate a terminal plate of the cell. Each cavity also may include a plurality of wedges around the periphery thereof. Each wedge may be shaped as a triangular web extending between the side wall and the cavity bottom. The wedges assist in holding a cell within a cavity of the holding board. By applying pressure and/or heat at the right places during assembly of the cells between the cell holding boards, the wedges are formed so as to eliminate rattle of the cell within the cavity, and accommodate variations in cell height.
Each holding board also includes a plurality of holes through the thickness thereof, but which are not located within the periphery of any cavity. Some of the through holes accommodate airflow through the holding board. This type of through hole may be of various sizes depending on its location relative to the cavities on the holding board, and may be of a slot type configuration, for example. This type of through hole, in conjunction with the openings in the end caps, provides an easy to manufacture mechanism for controlling the module""s thermal management. Of course any other suitable shape may be used for the airflow through holes. Other through holes accommodate tie rods, or other suitable means, which extend between the pair of holding boards to attach the holding boards together with the cells therebetween.
The second side of each holding board includes lugs for the attachment of an end cap. Because the lugs are formed as a part of the holding board, a reduced number of separate parts is necessary for assembly of the module, which is thereby facilitated. The lugs may have various configurations depending on how the end cap and the holding board are connected. In a first configuration, the lugs include threaded inserts therein which receive screws. The screws are inserted through an end cap, and into the threaded insert in the lug, to form the connection. In a second configuration, the lugs include blind holes therein, into which rivets are inserted. The rivets are inserted through an end cap, and into the hole in the lug. The rivets are then expanded within the hole in the lug to form the connection. In a third configuration, the lugs include two portions. A first portion extends from the second side of the holding board. A second portion, slightly smaller in periphery than the first portion, extends from the first portion. Because the second portion is smaller in periphery than the first, a shoulder, or stepped, portion is formed to about against an end cap. The second portion is inserted through an aperture in an end cap so as to extend therefrom. Then, the second portion is heated and deformed, as by a plastic riveting process, to form the connection. In the first and second configurations, the height of the lugs determines the height of the air manifold, whereas in the third configuration, the height of the first portion does so. Thus, the lugs also provide an easy manner in which to connect the end caps to the holding boards, especially in the third embodiment, while also easily maintaining an accurate manifold height.
The second side of each holding board also includes recesses shaped to accommodate electrical bus connectors which extend between pairs of the cells. The recesses do not extend through the entire thickness of the holding board, but are deep enough so that the bus connectors are below the second side of the holding board. In such a manner, the holding board itself provides electrical insulation between the connectors, each of which extend between a pair of cell terminals. The holding board itself also provides insulation between the connectors and the cell cases which are negatively charged. Because the cell holding board provides the necessary insulation, separate insulating materials are eliminated thereby reducing weight of the module. Further, the recesses are shaped so as to accommodate a complementarily shaped bus connector. Thus, the cell holding boards serve as a template, or map, for making the electrical connections between the cells in the module. Because the recesses only accommodate a complementarily shaped bus connector, assembly of the module is facilitated.
The cell assembly, comprised of a plurality of cells held between two holding boards, is inserted in a shell, and then the end caps are attached to the holding boards. The shell is dimensioned so that it is slightly shorter than the distance between the end caps after they have been attached to the holding boards. In such a manner, the shell does not receive any stress load applied to the end caps. That is, the shell is allowed to xe2x80x9cfloatxe2x80x9d between the end caps. Therefore, the shell may be made thin thus further reducing the weight of the module. Moreover, the thin shell has a simple overall shape which can easily be manufactured. Because the end caps take a force load, they may include stiffening ribs on a surface thereof.
In another embodiment, only one holding board is provided. With this arrangement the module does not stand alone, but is used as part of a battery pack.
b) Thermal Management Configuration
In the module, the cells are spaced from one another by a cell-to-cell distance measured between the outer periphery of one cell and the outer periphery of an adjacent cell. The cells adjacent the shell are spaced therefrom by a cell-to-shell distance. The temperature difference between the inner surface (at an inside diameter of a cell having a hollow core) and an outer surface (at an outside diameter of a cell having a hollow core) of each cell is xcex94T. An end cap is attached to each holding board with a space between the end cap and holding board. Within each end cap there are two ports. On one side of the module, the ports in one end cap are for air intake, whereas the ports in the opposite end cap are for exhaust. On the intake side, the space between the end cap and the holding board is an air manifold.
1) First Embodiment of the Module Thermal Management Configuration:
A battery module arrangement wherein uniform air velocity within the module is attained. To attain uniform air velocity distribution at all gaps between cells as well as between cells and the shell inside wall, an air intake manifold is designedxe2x80x94both analytically and experimentallyxe2x80x94with 2 ports of air intake on the intake end cap; each port having a set of openings with specially selected geometry and size on the side wall and the bottom. The air intake velocity distribution is controlled by the size and location of each intake port, the height of the air manifold created between the end cap inner surface and the top surface of the cell board, the size as well as geometry and location of each opening on the side wall and/or bottom of each air intake port. As a nonlimiting example, the manifold and intake ports are designed so that intake air entering at 5 m/s leaves on the exhaust side of the module at velocities ranging between 3.5 and 4.5 m/s measured at the exhaust point of cell-to-cell or cell-to-shell gaps. This has been verified experimentally for a selected manifold design. The air manifold, which is easily and accurately formed by the connection between the cell holding board and end cap, allows the control of the temperature within the cell by controlling the air flow rate.
2) Second Embodiment of the Module Thermal Management Configuration:
A battery module arrangement wherein uniform temperature distribution across each cell is attained. To attain uniform temperature distribution, the manifold height is minimized while still accommodating the cells, necessary hardware, and cell-to-cell connectors. The air intake ports do not need to include any specialized shape. The cell-to-cell and cell-to-shell distances were experimentally and analytically selected to maintain a uniform velocity of air through the cell assembly with a minimum pressure drop across the module and minimum air flow rate.
Because there is no specialized shape necessary for the air intake ports, there is no dedicated air intake and exhaust. That is, either side of the module may be the intake/exhaust, and air can flow through the module in either direction. With the above configuration, each cell within the module can be maintained at a predetermined xcex94T depending on the intake air flow rate.
c) Module Electrical Connector Configuration
There are two types of electrical connector within the module. A first type of connector extends between cells of the module. A second type of connector extends between common potentials of the electrically connected group of cells in the module and the desired load application outside of the module.
The first type of connector is an electrically conductive bus connector. Each bus connector is a strip of material having a first end and a second end. There is a hole on each the first end and the second end to accommodate a cell terminal stud. The first type of connector may be either straight, or include a curved section. The shapes of the connectors are complementary to the shape of the recesses in the cell holding boards to ensure that the cells are properly connected. A flag terminal is attached between the first and second ends of the strip. The flag terminal provides a simple connection between the module cells and the module electronic control system. The connectors are treated for anticorrosion. Because of their configuration, the bus connectors are easily made. Moreover, because of the simple connection provided by the flag terminal on the bus connector, assembly of the module is facilitated.
The second type of connector, a power connector, includes an L-shaped electrically conductive block. In the end of a first leg of the L-shaped block there is a blind threaded hole. The first leg extends through a square hole in an end cap of the module to enable connection to the threaded hole from outside of the module. The second leg of the L-shaped block includes a through hole in a side face thereof. A wire is connected to the hole in the second leg, and to a tab connection. The tab connection is then connected to the common potential of all the cells within the module.
d) Module Electronics Configuration
The module includes an electronic control system which is connected to the cells within the module so as to monitor voltage and temperature of each cell. Also, the electronic control system is used for communication with other modules, as well as cell balancing during the charge cycle of the module.